The present invention relates to a radio communication system, a radio communication device, and a radio communication method for realizing communication operation with low power consumption between devices at a relatively short distance from each other. Particularly, the present invention relates to a radio communication system, a radio communication device, and a radio communication method for performing non-contact, low power consumption, and high speed data transmission from a portable device that retains contents to a host device that manages contents.
More particularly, the present invention relates to a radio communication system, a radio communication device, and a radio communication method for performing non-contact, low power consumption, and high speed data transmission from a portable device that retains contents to a host device that manages contents, using a backscatter communication in which a reflected wave signal obtained by modulating an unmodulated carrier transmitted from a reflected wave reader side on the basis of transmission data on a reflector side is transmitted, and particularly to a radio communication system, a radio communication device, and a radio communication method for transmitting data of voice or music contents collected on a portable device side in a state of being reproducible by an audio reproducing device.
With the recent development of information technology, portable telephones and portable information terminals have become increasingly sophisticated. For example, these portable devices generally have functions of taking or recording contents such as a still image, a moving image, music and the like, and reproducing these recorded contents. In addition, a storage area built in a portable type audio reproducing device is increasing in capacity. That is, a style of carrying contents collected independently by a user has taken root.
On the other hand, contents collected within a portable device are usually closed within the portable device. That is, to listen to contents stored in the portable device on a stationary type reproducing device such as a television set, a video or an audio player or the like often requires a complicated operation of transferring the contents to a host device such as a PC or the like and then transferring the contents to a medium such as a CD, a DVD or the like. Although products connectable by a cradle or a docking type product or a wire cable such as a USB cable or the like have appeared as portable type audio reproducing devices, an installation place is limited, and there are problems of wear of contacts and limitation in shape.
Attention has been directed to a wireless connection system as a system for freeing users from wire connection. A wireless LAN, for example, allows a portable terminal to be moved relatively easily since most of a wire cable can be omitted in a work space such as an office or the like. Also, introducing a personal area network (PAN) is being considered to construct a small-scale wireless network between a plurality of electronic devices present around a person and thereby perform information communication.
Various radio communication systems using frequency bands that do not require a license from competent authorities, such as a 2.4 GHz band and a 5 GHz band, for example, are defined. Regular standards for wireless networks include, for example, IEEE (Institute of Electrical and Electronics Engineers) 802.11 (see, for example, International Standard ISO/IEC 8802-11: 1999(E) ANSI/IEEE Std 802.11, 1999 Edition, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications), HiperLAN/2 (see, for example, ETSI Standard ETSI TS 101 761-1 V 1.3.1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part 1: Basic Data Transport Functions or ETSI TS 101 761-2 V 1.3.1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part 2: Radio Link Control (RLC) sublayer), IEEE802.15.3, and Bluetooth communication. The wireless LAN has recently spread markedly partly because wireless LAN systems have become inexpensive and are incorporated in a PC as standard.
However, the wireless LAN was originally designed and developed assuming that the wireless LAN would be used by computers. Hence, when the wireless LAN is incorporated into a mobile type device, power consumption of the device becomes a problem. Many of IEEE802.11b wireless LAN cards commercially available now consume a power of 800 mW or more at a time of transmission, and a power of 600 mW or more at a time of reception. This power consumption is a heavy load on a battery-driven portable device.
Even when the transmission power is reduced by limiting the operation of a wireless LAN function to a short distance, the power consumption can be reduced to only about 80 percent. In particular, a transmission from an image input device such as a digital camera or the like to an image display device side, or a transmission of voice or music contents collected by a portable telephone, an IC recorder, or another portable information terminal to an audio reproducing device, for example, is a mode of communication in which transmission from the portable device side accounts for most of the communication as a whole. Radio transmission means with low power consumption is desired all the more because many portable devices are driven by a battery.
In Bluetooth communication, power consumption is not so heavy a load as in a wireless LAN system, but transmission speed is low at 720 kbps even at a maximum, which is inconvenient because it takes time to transmit recent high-quality images. In particular, it takes much time to transfer high-volume contents from a portable device to a host device.
Furthermore, contents including various media of still images, moving images, music, data and the like may be transmitted from a portable device side connected by radio. Since a data encoding method differs for each of these media, a host device side needs to determine a media type of a content transmitted thereto, and start an appropriate decoder according to a result of the determination to perform a decoding process and content reproduction. An embedded device limited in operational capability, for example, has another problem of a heavy overhead involved in the media type determination and the decoding process.
It is desirable to provide an excellent radio communication system, an excellent radio communication device, and an excellent radio communication method that make it possible to realize communication operation with low power consumption between devices at a relatively short distance from each other.
It is also desirable to provide an excellent radio communication system, an excellent radio communication device, and an excellent radio communication method that make it possible to perform non-contact, low power consumption, and high speed data transmission from a portable device that retains contents to a host device that manages contents.
It is also desirable to provide an excellent radio communication system, an excellent radio communication device, and an excellent radio communication method that make it possible to transmit data of voice or music contents collected on a portable device side in a state of being reproducible by an audio reproducing device.